Well... and there is a very cut and dry difference between Veganism and Vegetarianism... Vegetarians don't eat meat, for a variety of reasons ranging from health to ideological... but they are not necessarily opposed to animal products like eggs and milk and sometimes leather, and some which...
I would also be concerned about restricting the animal fat and proteins in small children's diets.
There's just too much peer reviewed scientific evidence supporting the need for those micronutrients found in meat and dairy for proper brain development. Your brain is after all... mostly fat...